Method for heating a delivery device for a reducing agent

ABSTRACT

A method for heating a delivery device for a reducing agent includes providing the delivery device with a return valve which is in an open position when an opening current is supplied to the return valve and which is in a closed position and operates as a heater when a heating current that is smaller than the opening current is supplied to the return valve. The return valve is preferably in heat-conducting contact with a metallic base plate of the delivery device.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation, under 35 U.S.C. §120, of copending International Application No. PCT/EP2010/062920, filed Sep. 3, 2010, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2009 041 179.8, filed Sep. 11, 2009; the prior applications are herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for heating a device for feeding liquid reducing agent and/or reducing agent precursor from a tank configuration.

The exhaust gas of internal combustion engines typically contains substances, the emission of which into the environment is undesirable. For example, in many countries, the exhaust gas of internal combustion engines may contain nitrogen oxide compounds (NO_(x)) only up to a certain limit value. Aside from engine-internal measures through which the emission of nitrogen oxide compounds is reduced by the selection of as suitable an operating point of the internal combustion engine as possible, after-treatment methods have also become established through which a further a reduction in nitrogen oxide emissions is possible.

One option for further reducing nitrogen oxide emissions is so-called selective catalytic reduction (SCR). In that case, a selective reduction of the nitrogen oxides to form molecular nitrogen (N₂) takes place by using a reducing agent. One possible reducing agent is ammonia (NH₃). In that case, ammonia is often not stored in the form of ammonia, but rather an ammonia precursor is stored which is converted into ammonia as required. The ammonia precursor is referred to as a reducing agent precursor. One significant possible reducing agent precursor which can be used in motor vehicles is urea ((NH₂)₂CO). Urea is preferably stored in the form of a urea-water solution. Urea and, in particular, urea-water solution is not harmful to health and is easy to distribute and store. A urea-water solution of that type with a urea content of 32.5% is marketed under the trademark “AdBlue.”

It is common for a urea-water solution to be carried on-board in a tank system in the motor vehicle and to be dosed in a portioned manner into the exhaust system through the use of an injection system including a pump and an injector. The consumption of urea for the reduction of undesired nitrogen oxide compounds in the exhaust gas amounts to up to 10% of the fuel consumption of the motor vehicle concerned. It is necessary for the reducing agent to be supplied to an injector at a defined pressure, for the portioned dosing of reducing agent. A problem with the provision of reducing agent at a defined pressure is that a urea-water solution generally freezes at low temperatures. A urea-water solution with a urea content of 32.5%, for example, freezes at temperatures of approximately −11° C. Frozen liquid urea generally cannot be delivered by a pump. At the same time, a pump device can easily be destroyed due to the ice pressure generated when freezing occurs. It is important for a pump device for urea to reach a state of operational readiness quickly even at low outside temperatures, because particularly large amounts of harmful emissions are generally released upon the commencement of driving with a motor vehicle. Furthermore, an injection system must not be damaged by the freezing of the reducing agent precursor contained therein.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method for heating a delivery device for a reducing agent, which overcomes the hereinafore-mentioned disadvantages and alleviates the highlighted technical problems of the heretofore-known methods of this general type. In particular, an especially advantageous method for heating a delivery device for reducing agent will be described.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method for heating a delivery device for a reducing agent. The method comprises providing the delivery device with a return valve having opened and closed positions, supplying an opening current to the return valve to operate the return valve in the opened position, supplying a heating current to the return valve to operate the return valve in the closed position as a heater, and setting the heating current to be smaller than the opening current.

In accordance with another particularly advantageous mode of the method of the invention, the return valve is in heat-conducting contact with a metallic base plate of the delivery device.

In accordance with a further particularly advantageous mode of the method of the invention, the return valve is in heat-conducting conduct with a housing of the delivery device.

As a rule, delivery devices for reducing agent have a return line, which is used for deaeration of the delivery device. A return line for deaeration is required, for example, if there is an air bubble in the components which should contain reducing agent. An air bubble is very difficult to transport, in particular with a pump, due to the pumping movement of the pump. This is true, in particular, for diaphragm pumps with passively acting valves, as are preferred for the delivery device according to the invention. The system can initially be operated through the return line in such a way that aspirated reducing agent is transported, at a low feed pressure through the suction pipe and the return line, back into the tank in the circuit until there is no more air in the delivery device. The return line is closed during normal operation of the delivery device, in which pressurized reducing agent is to be supplied, so that the pressure built up in the delivery device by the pump is not relieved. In this case, a return valve is provided for the return line or for the closing of the return line. For the described method, a valve is used which is opened when an electric current passes through it, and is closed when no electric current passes through it. The current flows through a magnetic coil in the return valve, which produces a magnetic force due to the current flow. The magnetic force in turn opens the valve. The use of such a valve is also therefore preferable because the normal state is the closed state, in which pressure is present in the delivery device, and the opened state occurs more rarely than the closed state. For this reason, energy can be saved by a return valve of this type. It is then particularly advantageous if the return valve can also be operated with a current which is not sufficient to open the return valve. In this case, the electrical, live windings in the return valve act like a resistance heater, which heats the delivery device and (directly by a metallic base plate) the possibly frozen reducing agent contained in the delivery device. Due to the heat-conducting connection from the return valve to the metallic base plate, and thus also to the metallic housing and to the metal suction pipe, it is also possible to heat the reducing agent in the reducing agent tank with the aid of a return valve operated as a heater.

The explanations presented herein regarding the return valve and the return line also constitute possible improvements to the delivery device described hereinafter.

This “passive” additional heating method can, in principle, also be combined with delivery devices which additionally include an active (electrically controllable) heater, in particular in the manner described hereinafter. In this respect, the method can be implemented, in particular, with the delivery device and/or tank configuration and/or vehicle described herein.

In accordance with an added particularly advantageous mode of the method of the invention, at least the opening current or the heating current is generated by a pulse-width modulation from a supply voltage. An electric opening voltage and/or an electric heating voltage is/are applied to the return valve in order to produce the opening current and/or the heating current.

The power supply of a motor vehicle generally provides only a specific supply voltage. For example, there are motor vehicles having a supply voltage of 12 volts. With pulse-width modulation a (predefined and/or desired) reduced voltage is produced from a (limited and/or uniform) supply voltage, with the aid of a specific electrical circuit, by pulsing the supply voltage over time. The level of the reduced voltage is then given according to the pulse width. A reduced voltage (in particular averaged over time) can thus be produced with a very low energy loss.

In accordance with an additional particularly advantageous mode of the method of the invention, the return valve includes a valve body and a spring element, and in the closed state the valve body is biased against a stop by the spring element. As a result of a suitably selected bias, it can then be ensured that the return valve is not already opened if (only) the heating current is applied.

In accordance with a concomitant particularly advantageous mode of the method of the invention, the heating current may be at least 10% smaller than the opening current. The heating current is more preferably at least 20% and particularly preferably at least 50% smaller than the opening current. For example, the opening current lies in the range above 500 mA [milliamperes]. A range below 200 mA [milliamperes], for example, is provided for the heating current. The opening current necessary to open the return valve is generally not precisely constant, but is slightly dependent on different ambient conditions. An ambient condition which is relevant in this case is temperature, for example. By appropriately selecting the heating current and considering at least one ambient condition, it can be ensured that the return valve is not opened unintentionally by the heating current.

The method according to the invention can be used, in particular, in the (sometimes referred to as “preferred”) delivery device which is described below.

The “preferred” device is a delivery device for a reducing agent, having a metallic housing including at least one externally fastened metallic suction pipe and an outer pressure line port, wherein a metallic base plate is disposed in the housing, at least one pump and ducts are provided at the metallic base plate, the suction pipe, the housing, the metallic base plate and the pump are in heat-conducting contact with one another and an elongate heating element is disposed alongside the suction pipe.

Within the context of the application, the expression “reducing agent” is also understood to mean a reducing agent precursor, such as a urea-water solution, preferably having a urea proportion of 32.5% by weight.

A fundamental basic concept of the “preferred” delivery device is that it is to be made particularly easy to heat the device when the reducing agent freezes in the delivery device. For this reason, all components filled during operation with liquid reducing agent are fastened on a common metallic base plate, through which they are in heat-conducting contact with one another. The device can thus be heated efficiently by a single elongate heating element (parallel) along the suction pipe.

The suction pipe of a “preferred” delivery device is generally disposed in a tank for reducing agent. Since the heating element is disposed beside and/or parallel to the suction pipe along the suction pipe, the reducing agent in a tank which is located around the suction pipe is also heated efficiently. On one hand, the reducing agent provided there can thus be melted quickly and therefore also aspirated quickly and easily. On the other hand, a sheet of ice possibly formed in the reducing agent tank around the suction pipe is melted so that a vacuum, which would hamper or even prevent the feeding of reducing agent from the reducing agent tank, cannot form beneath the sheet of ice as a result of the aspiration.

The heating element is preferably braced against the suction pipe by a clamp or clip. The clamp or clip is made of heat-conducting material, for example aluminum. It is formed in such a way that it lies extensively against an inner face of the suction pipe so that there is a good transfer of heat from the clamp to the casing pipe. For example, the heating element may be brazed, soldered or welded onto the clamp so that there is also a good transfer of heat between the heating element and the clamp. The clamp is preferably formed as a bent sheet metal with a radius in the relaxed state which is slightly greater than the radius of the inner face of the suction pipe. The clamp is thus seated under tension in the suction pipe and does not have to be fixed therein in a cohesively bonded manner. The clamps may possibly include bores so as to adjust the transfer of heat from the heating element to the suction pipe.

The mounting of the important components containing reducing agent, that is to say above all the pump and the ducts, on a metallic base plate also enables simple assembly of the delivery device according to the invention. It is not necessary to assemble these components directly in the housing. Instead, they can be preassembled on the metallic base plate and then introduced as a module into the metallic housing.

The “preferred” delivery device is particularly advantageous if ducts are formed in the metallic base plate, and if the suction pipe, the pump and the port are connected fluidly in the metallic base plate through the ducts.

The (one-piece) metallic base plate may be formed as a milled and/or cast part, for example. Ducts can thus be produced easily, for example in the form of bores, in the metallic base plate. In a cast part, the ducts can be produced easily with the aid of casting cores. Providing the fluid connections between the individual components of the delivery device directly by ducts in the metallic base plate reduces the number of necessary individual parts and thus contributes to simplifying the assembly of the device and thus to making it more cost effective. It is therefore also possible to introduce heat quickly from the base plate into the ducts, so that any reducing agent present in this case will be quickly melted.

The metallic base plate can be provided with protruding bearing surfaces so that components (such as the pump, valves and pressure sensors) can be assembled or replaced from above, without the metallic base plate having to be removed from the metallic housing.

The metallic base plate (and possibly further/all components stated herein as being metal) is preferably (at least at the surface, but more preferably solidly or completely) produced from or with steel. Aluminum may possibly also likewise be used as a material for the metallic base plate. A particularly good conduction of heat from the heating element to the individual components of the delivery device can thus be provided by the metallic base plate.

The metallic housing is preferably produced by deep-drawing (as a deep-drawn component). In order to attach the suction pipe to the metallic housing, the housing preferably includes a protruding flange which centers the suction pipe on the metallic housing. The suction pipe should be connected to the metallic housing by brazing, soldering or laser-welding.

All of the metal components of the “preferred” delivery device are preferably manufactured from corrosion-resistant austenitic steel (for example from one of the steels having the material number 1.4301 or 1.4828 according to the German “Stahlschlüssel” or key to steel) or alternatively from corrosion-resistant ferrite steel (for example from the steel having the material number 1.4607 according to the German “stahlschlüssel” or key to steel). The metal components include, in particular, the base plate, a filter housing, the suction pipe and the housing of the filter device. The base plate and/or a filter housing can be manufactured from cast steel or cast aluminum and possibly additionally include a coating.

The “preferred” device is also particularly advantageous if a metal filter housing is connected in a heat-conducting manner to the base plate, with a filter being located or able to be located in the filter housing.

Liquid reducing agent often contains relatively small particles which could damage components of the delivery device. For example, particularly sensitive components of the delivery device are the valves of the pump or injector with which reducing agent can be fed into the exhaust system of an internal combustion engine. For this reason, it is advantageous to filter reducing agent. Liquid reducing agent is also stopped in the filter or in the filter housing surrounding the filter, and therefore freezing occurs in this case, too. It is thus advantageous to link the filter housing to the metallic base plate in a heat-conducting manner so that the filter housing can also be heated efficiently and frozen reducing agent in the filter housing is thus melted.

The metallic filter housing and the base plate can also be a common component. This component can be milled or cast from a metal block, for example. A particularly good conduction of heat from the metallic filter housing to the base plate and vice-versa can thus be achieved. At the same time, the complexity of the assembly of the delivery device is reduced with a common component of this type.

The “preferred” delivery device is furthermore particularly advantageous if the suction pipe extends into the filter housing together with the heating element.

On one hand, a configuration of this type enables a particularly efficient heating of the filter housing. The filter housing is the component in the delivery device which includes the greatest volume filled with reducing agent. A particularly large input of thermal energy is accordingly necessary precisely in this case so as to melt the reducing agent, if it is frozen.

Allowing the suction pipe to also protrude into the filter housing has various advantages. On one hand, the connection between the housing/metallic base plate and the suction pipe is much more mechanically stable. Since the suction pipe extends into the filter housing, greater bending moments can be transferred from the suction pipe into the housing. These bending moments become effective, for example, by striking the suction pipe during the assembly process or by acceleration processes during travel of the motor vehicle.

The filter is provided above all for the protection of the subsequent functional components of the delivery device. The filter is therefore possibly the first functional component which is disposed along the path of the reducing agent from a tank towards the pressure line port of the delivery device. It is thus particularly advantageous to allow the suction pipe to extend directly into the filter housing, because a particularly compact and integrated construction of the delivery device according to the invention is thus enabled.

The “preferred” delivery device is furthermore particularly advantageous if a metal coarse filter for particles larger than 30 μm (micrometers) is formed on the suction pipe.

The filter, which can be disposed in the filter housing on the metallic base plate, is generally constructed for filtering substantially smaller particles. For example, particles having a diameter less than 10 μm (micrometers) and preferably particles having a diameter less than 3 μm (micrometers) are to be retained by the filter.

A metallic coarse filter provided on the suction pipe can ensure that the filter provided in the housing is not blocked prematurely. The service life of the filter in the housing can thus be increased considerably, so that the maintenance cycles for the delivery device according to the invention can thus be increased.

The “preferred” delivery device is also particularly advantageous if the metallic coarse filter includes a screen which surrounds a suction end of the suction pipe in a pot-like or cup-like manner. The suction end is generally the lower end of the suction pipe opposite the housing of the delivery device.

Reducing agent is generally aspirated into the suction pipe at one suction end of the suction pipe. A screen as a component of the metallic coarse filter is particularly cost effective to produce. In addition, a suitably dimensioned screen reduces the sloshing movements of the reducing agent in a reducing agent tank directly around the suction pipe. A surge reservoir provided in the tank to reduce this sloshing movement may even be dispensed with if the screen is suitably formed. Sloshing movements in a tank in a motor vehicle are triggered during driving by accelerations when accelerating, braking or driving around corners.

The coarse filter and/or screen are also preferably fastened to the heating element so as to be in heat-conducting contact therewith.

The “preferred” delivery device is also particularly advantageous if at least one level sensor electrode, with which a fill level of the reducing agent in the tank can be determined, is fastened on the suction pipe.

For example, a single punctiform or point-like or button-like level sensor electrode can determine whether or not a reserve fill level in the reducing agent tank has been undershot. If two punctiform or button-like level sensor electrodes are provided, it can additionally be determined whether or not a fill level of the reducing agent tank is present which corresponds to a full reducing agent tank. The fill level of the system can be established in the region between the two level sensor electrodes with the aid of software which monitors the amounts of reducing agent injected into the exhaust system. An elongate level sensor electrode can also be provided which continuously determines the fill level in the reducing agent tank directly. Level sensor electrodes can generally determine the fill level by the conductivity of the reducing agent.

A (single punctiform or button-like) level sensor electrode can also be attached to the metallic housing of the delivery device. The metallic housing is then disposed, at least in part, inside a tank configuration for a reducing agent. The tank configuration can be filled with reducing agent until the reducing agent is also present around the metallic housing. Such a fill level of a tank configuration can also be determined with the aid of a level sensor electrode attached on the metallic housing of the delivery device.

The “preferred” delivery device is also particularly advantageous if the heating element is a PTC (positive temperature coefficient) heating element.

PTC heating elements are based on a PTC heat conductor. A heat conductor of this type increases its electrical resistance significantly from a specific temperature. A PTC heating element thus adjusts itself to a certain heating temperature. In this case, precisely only one PTC heating element is preferably provided along the suction pipe and actively heats the delivery device as required.

The required heating effect may possibly also be assisted, at least in part, by the waste heat of the pump, valve, filter, etc. during operation.

The “preferred” delivery device is also particularly advantageous if the suction pipe includes an inner conduit pipe and an outer holding pipe, wherein the heating element is disposed between the conduit pipe and the holding pipe.

On one hand, an outer holding pipe of this type around the inner conduit pipe and heating element increases the mechanical strength of the suction pipe protruding from the housing. On the other hand, a cylindrical outer shape of the suction pipe can be selected, although the heating element is also provided in the suction pipe in addition to the conduit pipe.

All parts of the suction pipe are preferably made of metal and include mutual metal contact points so that an efficient exchange of heat between the components is possible and heat from the heating element is easily transferred to the outer holding pipe. The outer holding pipe is generally in contact with the surrounding reducing agent in a tank and can thus heat this reducing agent.

Furthermore, a tank configuration including a reducing agent tank with a tank opening and a “preferred” delivery device is described herein, wherein the tank opening is closed by the delivery device, and the suction pipe extends towards the base of the reducing agent tank.

A tank configuration for a reducing agent must be closed during operation so that no reducing agent can slosh out of the tank configuration. At the same time, a reducing agent tank should have a closable opening of sufficient size, through which the tank can be cleaned. It has already been described further above that particles are generally contained in the reducing agent and may contaminate the reducing agent tank. Closing this opening in the tank simultaneously with the housing of a delivery device can be achieved in a particularly technically simple and particularly space-saving manner.

The opening in the tank is preferably closed by the housing of the delivery device in such a way that the suction end of the suction pipe is located in the vicinity of the base of the tank and, in particular, does not contact the base of the tank. A separate support for receiving the suction end can also be provided on or in the base of the tank and, for example, can take up forces on the suction pipe which are produced, for example, by accelerations during operation of a motor vehicle. The tank for the reducing agent is preferably manufactured from plastics material. The opening in the tank closed by the housing may include a screw plug, wherein the housing may be formed with a corresponding thread. In addition, a seal may be provided at the opening, with the seal being pinched or pressed together by insertion of the housing into the opening, and thus sealing the opening in the housing.

The tank configuration is also preferable if more than 50% of the housing is disposed beneath the tank opening. Where possible, even up to 80% and, in particular, up to approximately 100% of the housing of the delivery device should be disposed beneath the tank opening.

This configuration of the housing of the delivery device enables a particularly space-saving configuration of the reducing agent tank and the housing. The installation space available for the reducing agent tank can be filled completely by the reducing agent tank itself. The volume of this tank is available for the reducing agent and merely the volume of the delivery device has to be subtracted. With a completely filled tank, the tank may even be filled to the extent that reducing agent is present around the housing. With this configuration of the housing of the delivery device in the tank, it is particularly advantageous if the housing, together with the suction pipe, is connected in a heat-conducting manner to the metallic base plate. Starting from the (metallic) housing, it is then also possible to melt through a sheet of ice present in the reducing agent tank. This is to be achieved with fill levels of reducing agent in the tank at the level of the housing. It is particularly advantageous if the housing and the tank opening are round. The closure of the reducing agent tank by the housing should be as tight as possible. Round, flat contact surfaces between the housing and the tank opening generally make it possible to produce a tight connection in a particularly cost-effective manner.

The “preferred” delivery device may possibly also be described as an extraction pipe having two different diameters, in which all components for providing pressurized, liquid reducing agent are integrated. The diameter of the suction pipe represents the first diameter of the extraction pipe. The diameter of the housing is the second diameter of the extraction pipe. The necessary functional components (such as pump, lines, filter, etc.) can be placed easily in the larger diameter of the housing. An extraction pipe having two different diameters, in which all components for providing pressurized, liquid reducing agent are integrated, is also an invention independently of the features already described. This invention can, of course, be combined with all preferred embodiments of the “preferred” delivery device described herein.

The tank configuration is also particularly advantageous if the suction pipe has a suction end which is positioned in a depression in the base of the tank configuration. It is generally particularly advantageous if the reducing agent is aspirated at the lowest point of the tank, because the tank can then be emptied practically completely and the entire volume of the tank can be utilized. At the same time, a depression in the base of the tank can act as a surge reservoir, which ensures that reducing agent is always present around the suction end of the suction pipe, even in the event of sloshing movements in the tank.

In particular, the invention is used in a motor vehicle including an internal combustion engine with an exhaust system which is constructed to carry out a selective catalytic reduction of nitrogen oxide compounds, wherein the motor vehicle includes a tank configuration and/or a “preferred” delivery device described herein.

The embodiments and advantages described for the delivery device can be transferred in a similar manner to the motor vehicle, to the method according to the invention and to the tank configuration. The same applies to the advantages and embodiments presented for the tank configuration, which are transferrable to the “preferred” delivery device, to the method according to the invention and to the motor vehicle. The advantages and embodiments described for the method according to the invention and for the motor vehicle are transferrable to the “preferred” delivery device and to the tank configuration.

Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the steps specified individually in the claims can be combined in any technically feasible manner and can be supplemented by explanatory facts from the description, in which further variants of the invention are presented.

Although the invention is illustrated and described herein as embodied in a method for heating a delivery device for a reducing agent, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, perspective view of a delivery device;

FIG. 2 is a longitudinal-sectional view of a first variant of the delivery device;

FIG. 3 is a cross-sectional view of a further delivery device, which is taken along a line III-III of FIG. 2, in the direction of the arrows;

FIG. 4 is a longitudinal-sectional view of a further embodiment of a delivery device;

FIG. 5 is a longitudinal-sectional view of yet a further embodiment of a delivery device;

FIG. 6 is a side-elevational view of part of a motor vehicle having a tank configuration which has a delivery device; and

FIG. 7 is an enlarged, cross-sectional view of a return valve for the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a delivery device 1. The delivery device 1 has a metallic housing 6 and a metallic suction pipe 4. A coarse filter 16, which has a screen 17, is provided at a suction end 18 of the suction pipe 4. The housing 6 has a flange 12 with which the housing 6 can be sealed off against a corresponding flange, for example on a tank configuration. A cover 15, which is also provided in the housing 6, can be opened and servicing of the delivery device 1 can, for example, take place therethrough. It is, for example, possible for a non-illustrated filter in the delivery device 1 to be exchanged through the cover 15.

FIG. 2 is a sectional view through a delivery device 1. This figure, too, shows the housing 6 and the suction pipe 4. Important components of the delivery device are fastened to a metallic base plate 7 which is provided in the housing 6. FIG. 2 shows a (metallic) filter housing 13 and a return valve 20 as components. A filter 14 is also provided in the filter housing 13. Direct access to the filter housing 13 is possible through the cover 15 in the housing 6, in such a way that the filter 14 can be exchanged quickly and easily. In an advantageous embodiment, the filter housing 13 is sealed off against the housing 6 in such a way that the interior space of the filter housing 13 is closed off with respect to the interior space of the housing 6 even when the cover 15 is open. A reducing agent in the housing 6 can thus be prevented from reaching locations which it must not reach, even during an exchange of the filter 14. The possibility of exchanging the filter 14 through a cover 15 is particularly advantageous because the filter 14 is generally the component which must be serviced most frequently in the delivery device.

In a variant of the delivery device 1, the filter 14 may be constructed as a filter cartridge. The delivery device 1 and the filter 14 may each have connection elements which, when the filter 14 is installed, produce at least a fluidic connection between the filter 14 and the delivery device 15. The connection elements may furthermore be constructed in such a way that both the filter 14 and also the delivery device 1 are closed off in a fluid-tight manner when the filter 14 is removed from the delivery device 1. It can thus be ensured that reducing agent does not emerge either from the delivery device 1 or from the filter 14 when the filter 14 is removed from the delivery device 1. In such an embodiment, an exchange of the filter 14 can be carried out in a safe and reliable manner.

A compensation element 36 may also be provided in the cover 15. A compensation element 36 of that type may, for example, take the form of elastic filler material (for example porous rubber) in order to compensate expansions of the reducing agent when it freezes, so that the delivery device 1 according to the invention is not damaged by the freezing process.

In an advantageous embodiment of the delivery device 1, all of the components of the filter device 1 aside from the filter 14 are constructed and dimensioned in such a way that they need not be exchanged over the service life of the delivery device 1, and the housing 6 of the filter device 1 (aside from the cover 15) is constructed so as to be sturdy, durable and in such a way that it cannot be opened without being destroyed.

It can also be seen that the flange 12 of the housing 6 is provided for connection of the housing 6, for example to a reducing agent tank. A pressure line port 5, through which pressurized reducing agent can be conveyed out of the delivery device 1, is provided on top of the housing 6. The pressure line port 5 may be provided directly on the metallic base plate 7, or integrally cast with the metallic base plate 7 if the latter is formed as a cast part. It is thus possible to attain very good heat transfer between the pressure line port 5 and the metallic base plate 7. The pressure line port 5 can then be jointly heated passively (through the use of heat conduction) through the metallic base plate 7. The pressure line port 5 is preferably produced from a material with good heat conductivity. The pressure line port 5 is preferably produced from aluminum or stainless steel. A return line 21 exits the housing 6 at the bottom. The reducing agent can pass from the delivery device 1, through the return line 21, back into a reducing agent tank when the return valve 20 is open.

The suction pipe 4 is constructed from an inner conduit pipe 25 and an outer holding pipe 26. A (single PTC) heating element 24, which is provided between the inner conduit pipe 25 and the holding pipe 26, extends along the suction pipe 4 into the housing 6 and/or the filter housing 13. The fill level of reducing agent can be determined through the use of level sensor electrodes 22, which are also provided on the suction pipe 4. As is seen in FIG. 2, the coarse filter 16 having the screen 17 is also provided at the suction end 18 of the suction pipe 4.

An inner filter housing 40, for accommodating the heating element 24, is generally situated in the filter housing 13, as an extension of the outer holding pipe 26 of the suction pipe 4. A connecting point 39 between the inner filter housing 40 and the inner conduit pipe 25 is generally very important for the leak-tightness of the delivery device 1. The connecting point 39 should be either brazed, soldered or laser-welded and/or formed with at least one 0-ring seal. The leak-tightness of the connecting point 39 is necessary because, otherwise, reducing agent could penetrate into the housing 6 of the delivery device 1 during operation. If the connecting point 39 is brazed, soldered or laser-welded, the heating element 24 cannot be accessed after assembly without destroying the delivery device 1. If the connecting point 39 is formed with an 0-ring seal, the heating element 24 of the delivery device 1 can be exchanged.

In the embodiment of the delivery device 1 shown herein, the suction of reducing agent takes place at the suction end 18 of the suction pipe 4, through radial bores 37. The radial bores 37 extend through the outer holding pipe 26, the inner conduit pipe 25 and a plug 38 which connects the outer holding pipe 26 and the inner conduit pipe 25 to one another in a lower region at the suction end 18 and which at the same time seals off an intermediate space between the outer holding pipe 26 and the inner conduit pipe 25 with respect to the environment. A plurality of radial bores 37 may be provided at the suction end 18. The plug 38 is preferably metallic and brazed, soldered or welded to the inner conduit pipe 25 and to the outer holding pipe 26.

FIG. 3 shows a further sectional view through the delivery device 1, in which the section through the housing 6 has been selected as indicated by a line III-III in FIG. 2. A pump 8, the return valve 20, a pressure sensor 19 and the filter housing 13 are provided on the metallic base plate 7, as is visible in the housing 6 in FIG. 3. Fluidic connections are produced between the pump 8, the pressure sensor 19, the filter housing 13 and the return valve 20, through ducts 9 provided in the metallic base plate 7. The filter 14 is disposed in the filter housing 13. As viewed from above, it is possible to see the suction pipe 4 and the heating element 24 within the filter housing. The individual components of the system such as, for example, the filter housing 13, the housing 6 or the suction pipe 4, are in heat-conducting contact through contact surfaces 29. A transfer of heat from one component to an adjacent component is also possible through the contact surfaces 29. If components of the system are disposed so as to be spaced apart from one another for structural reasons, a heat-conducting connection may also be produced through the use of heat bridges 30. Such a heat bridge 30 is illustrated herein by way of example between the metallic base plate 7 and the pump 8.

FIGS. 4 and 5 are sectional views through further preferred embodiments of the delivery device 1. Both figures show the housing 6, the pressure line port 5, the filter housing 13, the cover 15, the flange 12 and the return valve 20. The suction pipe 4 with the inner conduit pipe 25, the outer holding pipe 26 and the heating element 24, are also visible. In both embodiments according to FIGS. 4 and 5, the coarse filter 16 having the screen 17 is provided at the suction end 18 of the suction pipe 4.

As a special feature, the embodiment according to FIG. 4 has a return line 21 which leads into an intermediate space between the coarse filter 16 and the suction pipe 4. As a result of this special layout of the return line 21, it is possible for the coarse filter 16 to be flushed out from the inside when reducing agent is returned through the return line 21. In this way, it is possible to ensure particularly good permeability of the coarse filter 16 even over a long operating period of the delivery device 1.

The embodiment according to FIG. 5 has, as a special feature, an elongate level sensor electrode 22 through which a fill level 23 (shown in FIG. 6) of a reducing agent tank can be determined in a continuous fashion. Furthermore, in the embodiment according to FIG. 5, a filter 14 is provided in the intermediate space between the coarse filter 16 and the suction line 4 at the suction end 18 of the suction line 4. In this way, it is possible to dispense with a filter 14 in the filter housing 13. This makes the system according to FIG. 5 particularly inexpensive. If an opening is additionally provided in a reducing agent tank below the suction end 18, an exchange of the filter 14 can be carried out in a particularly simple manner without it being necessary to open the delivery device 1 through the use of the cover 15. The opening of a tank in the downward direction furthermore has the advantage of permitting deposits which form in the tank to be discharged out of the tank very easily.

The various features of the embodiments of the delivery device shown in FIGS. 2, 4 and 5 may be combined with one another in any desired technologically meaningful way within the context of the invention.

FIG. 6 shows a motor vehicle 34 having an internal combustion engine 35 and an exhaust system 33. Reducing agent is supplied into the exhaust system 33 through an injector 32. The exhaust system 33 is provided for carrying out a selective catalytic reduction. The motor vehicle 34 has a tank configuration 27 in which a delivery device 1 is disposed. The delivery device 1 closes off an opening 10 of a reducing agent tank 2 of the tank configuration 27 in such a way that a flange 12 of the delivery device 1 connects to a corresponding counterpart flange at the opening 10. The cover 15, the suction pipe 4, the coarse filter 16, the return line 21 and the housing 6, are also visible on the delivery device 1 in FIG. 6. Furthermore, the fill level 23 in the reducing agent tank 2 can be determined through the use of a level sensor electrode 22 fastened to the suction pipe 4. The reducing agent tank 2 is provided with a tank bottom 11 which has a depression 28 in the region of the suction end 18 of the suction line 4, in such a way that the tank can be virtually completely emptied. A tank heating device 31, which may be provided in the reducing agent tank 2, serves to heat the reducing agent in the tank in addition to the heating action provided through the use of the delivery device 1. Such heating of the reducing agent in the reducing agent tank 2 may be realized, for example, through the use of cooling water. The pressure line port 5 of the delivery device 1 is adjoined by a line 3 through which pressurized reducing agent is delivered by the delivery device 1 to the injector 32 and into the exhaust system 33.

A double O-ring seal composed of two parallel O-ring seals disposed preferably concentrically adjacent one another, is generally provided between the flange 12 of the delivery device 1 and the opening 10 of the reducing agent tank 2 of the tank configuration 27. A double O-ring seal of that type can also seal off the connection between the delivery device 1 and the reducing agent tank 2, if that connection lies below the maximum fill level 23 of the reducing agent tank 2. The reducing agent tank 2 is generally composed of metal in the region of the opening 2. The sealing through the use of the O-ring seal consequently takes place between two metallic surfaces. Metallic surfaces can generally be produced with greater precision than plastic surfaces. Accordingly, with a double O-ring seal, correspondingly leak-tight sealing can be realized in this case. The connection between the delivery device 1 and the reducing agent tank 2 at the opening 10 is realized preferably through the use of an SAE screw connection.

FIG. 7 shows a return valve 20, with which the method according to the invention can be carried out in a particularly advantageous manner. The return valve 20 includes a valve body 41, which is biased against a stop 43 by a spring element 42. In the biased state, the return valve 20 is closed. In addition, the return valve 20 has a coil 44, with which the valve body 41 can be moved from a closed position, against the action of the spring element 42, into an opened position.

The delivery device and the tank configuration are of particularly simple and inexpensive construction and simultaneously permit a high level of safety and high reliability in the provision of reducing agent. The delivery device and tank configuration therefore represent a considerable improvement over the prior art. 

1. A method for heating a delivery device for a reducing agent, the method comprising the following steps: providing the delivery device with a return valve having opened and closed positions; supplying an opening current to the return valve to operate the return valve in the opened position; supplying a heating current to the return valve to operate the return valve in the closed position as a heater; and setting the heating current to be smaller than the opening current.
 2. The method according to claim 1, which further comprises placing the return valve in heat-conducting contact with a metallic base plate of the delivery device.
 3. The method according to claim 1, which further comprises placing the return valve in heat-conducting contact with a housing of the delivery device.
 4. The method according to claim 1, which further comprises generating at least the opening current or the heating current by pulse-width modulation from a supply voltage.
 5. The method according to claim 1, which further comprises providing the return valve with a valve body, a spring element and a stop, and biasing the valve body against the stop with the spring element in the closed position.
 6. The method according to claim 1, which further comprises setting the heating current to be at least 10% smaller than the opening current. 